python爬取网站页面时，部分标签无指定属性而报错

在写爬取页面a标签下href属性的时候，有这样一个问题，如果a标签下没有href这个属性则会报错，如下：

百度了有师傅用正则匹配的，方法感觉都不怎么好，查了BeautifulSoup的官方文档，发现一个不错的方法，如下图：

官方文档链接：https://beautifulsoup.readthedocs.io/zh_CN/v4.4.0/

has_attr() 这个方法可以判断某标签是否存在某属性，如果存在则返回 True 

解决办法：

为美观使用了匿名函数

soup_a = soup.find_all(lambda tag:tag.has_attr('href'))

最终实现爬取页面 url 脚本如下：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author:Riy

import time
import requests
import sys
import logging
from bs4 import BeautifulSoup
from requests.exceptions import RequestException
from multiprocessing import Process, Pool


logging.basicConfig(
    level=logging.DEBUG,
    format='%(levelname)-10s: %(message)s',
)


class down_url:
    def download(self, url):
        '''爬取url'''
        try:
            start = time.time()
            logging.debug('starting download url...')
            response = requests.get(url)
            page = response.content
            soup = BeautifulSoup(page, 'lxml')
            soup_a = soup.select('a')
            soup_a = soup.find_all(lambda tag:tag.has_attr('href'))
            soup_a_href_list = []
            # print(soup_a)
            for k in soup_a:
                # print(k)
                soup_a_href = k['href']
                if soup_a_href.find('.'):
                    # print(soup_a_href)
                    soup_a_href_list.append(soup_a_href)
            print(f'运行了{time.time()-start}秒')
        except RecursionError as e:
            print(e)
        return soup_a_href_list


    def write(soup_a_href_list, txt):
        '''下载到txt文件'''
        logging.debug('starting write txt...')
        with open(txt, 'a', encoding='utf-8') as f:
            for i in soup_a_href_list:
                f.writelines(f'{i}
')
        print(f'已生成文件{txt}')


    def help_memo(self):
        '''查看帮助'''
        print('''
        -h or --help 查看帮助
        -u or --url  添加url
        -t or --txt  写入txt文件
        ''')


    def welcome(self):
        '''欢迎页面'''
        desc = ('欢迎使用url爬取脚本'.center(30, '*'))
        print(desc)


def main():
    '''主函数'''
    p = Pool(3)
    p_list = []
    temp = down_url()
    logging.debug('starting run python...')
    try:
        if len(sys.argv) == 1:
            temp.welcome()
            temp.help_memo()
        elif sys.argv[1] in {'-h', '--help'}:
            temp.help_memo()
        elif sys.argv[1] in {'-u ', '--url'} and sys.argv[3] in {'-t', '--txt'}:
            a = temp.download(sys.argv[2])
            temp.write(a, sys.argv[4])
        elif sys.argv[1] in {'-t', '--txt'}:
            print('请先输入url！')
        elif sys.argv[1] in {'-u', '--url'}:
            url_list = sys.argv[2:]
            print(url_list)
            for i in url_list:
                a = p.apply_async(temp.download, args=(i,))
                p_list.append(a)
            for p in p_list:
                print(p.get())
        else:
            temp.help_memo()

            print('输入的参数有误！')
    except Exception as e:
        print(e)
        temp.help_memo()


if __name__ == '__main__':
    main()